"A family of five has an average (arithmetic mean) age of 20 years and a median age also 20 years."
By this information we can get 2 insights:
- If we have an odd number of elements, the median will be the central value. Therefore, the 3rd element (when ordered) has 20 years.
- If the average is 20, the sum of all ages is 5*20 = 100.
"Each member of the family is a whole number of years old, and all have different ages. Also, the oldest member is 16 years older than the youngest member."
Ok. Now we have, ordered, something like:
A, X, 20, Y, A+16 where X + Y + 2A + 16 = 80
"Select for Minimum the minimum possible age of the oldest member of the family, and select for Maximum the maximum possible age of the oldest member. Make only two selections, one in each column."
To maximize a number, we normally need to minimize the other numbers. In this case, however, we have a constraint about the lowest value: it needs to be only 16 lower than the maximum. But we can minimize the "Y" and try to minimize "X" so we can use the values between A and A+16.
Let's try values: the greatest option is 30. If we plug it, we'll have:
(30-16), X, 20, Y, 30
14, X, 20, Y, 30
X + Y = 100 - 64 = 36
If we set X = 14 + 1 = 15, we have 21 to set as Y. This fits perfectly:
14, 15, 20, 21, 30
So, 30 is the maximum possible value.
To minimum, let's try 25 (an intermediate option, so if it doesn't work we cut out half of the possibilities):
(25-16), X, 20, Y, 25
9, X, 20, Y, 25
X + Y = 100 - 54 = 46
If we set X = 20 - 1 = 19 (the maximum X value), we need to have Y = 46 - 19 = 27, that is greater than 25. So, we can not have a valid set with 25 as the oldest member.
Let's try 26 now:
(26-10), X, 20, Y, 26
10, X, 20, Y, 26
X + Y = 100 - 56 = 44
If we set X = 20 - 1 = 19 (the maximum X value), we need to have Y = 44 - 19 = 25, that is smaller than 26. So, we can have a valid set with 26 as the oldest member.
Therefore:
Answers =
Minimum: 26
Maximum: 30